Gas turbine engines are known to include a compressor for compressing air, a combustor for producing a hot gas by burning fuel in the presence of the compressed air produced by the compressor, and a turbine for expanding the hot gas to extract shaft power. Gas turbine engines using annular combustion systems typically include a plurality of individual burners disposed in a ring about an axial centerline for providing a mixture of fuel and air to an annular combustion chamber disposed upstream of the annular turbine inlet vanes. Other gas turbines use can-annular combustors wherein individual burner cans feed hot combustion gas into respective individual portions of the arc of the turbine inlet vanes. Each can includes a plurality of main burners disposed in a ring around a central pilot burner, as illustrated in U.S. Pat. No. 6,082,111.
The design of a gas turbine combustor is complicated by the necessity for the gas turbine engine to operate reliably with a low level of emissions, such as oxides of nitrogen (NOx), at a variety of power levels. In addition, it is important to ensure the stability of the flame to avoid unexpected flameout and damaging levels of acoustic vibration. A relatively rich fuel/air mixture will improve the stability of the combustion process but will have an adverse affect on the level of emissions. A careful balance must be achieved among these various constraints in order to provide a reliable machine capable of satisfying very strict modern emissions regulations over a wide range of loading conditions. A pilot flame is commonly used to stabilize the flame.
Staging is the delivery of fuel to burners of the gas turbine engine through at least two separately controllable fuel supply systems or stages. Staging is known as a method to control combustion in a gas turbine combustor. A staged gas turbine combustor pilot is described in U.S. Pat. No. 6,877,307 as having a premix stage wherein air and fuel are premixed prior to being combusted in a pilot combustion region to achieve reduced pollutant emission. In a multi-stage gas turbine engine, the fuel stages are typically operated according to preset fuel flow values, or fuel fractions of the total fuel provided to the engine, corresponding to values in a fuel flow table that specifies fuel amounts delivered to the respective stages. The values stored in fuel flow table may correspond to certain load ranges and environmental operating conditions, such as ambient temperature and/or humidity.
Traditionally, gas turbine engine settings, such as fuel flow settings, for a land-based powder generation turbine are manually “tuned” by a combustion engineer during the start-up of the power plant in order to satisfy appropriate emissions criteria without exceeding dynamic operating condition limitations.